With increasing development of science and technology, diverse electronic devices are used to achieve various purposes. An electronic device comprises a plurality of electronic components. Generally, different kinds of electronic components are operated by using different voltages.
As known, a power supply is essential for many electronic devices such as personal computers, industrial computers, servers, communication products or network products. Usually, the user may simply plug a power supply into an AC wall outlet commonly found in most homes or offices so as to receive an AC voltage. The power supply will convert the AC voltage into a regulated DC output voltage for powering the electronic device. The regulated DC output voltage is transmitted to the electronic device through a power cable.
Generally, power supply apparatuses are classified into two types, i.e. a linear power supply apparatus and a switching power supply (SPS) apparatus. A linear power supply apparatus principally comprises a transformer, a diode rectifier and a capacitor filter. The linear power supply apparatus is advantageous due to its simplified circuitry and low fabricating cost. Since the linear power supply apparatus has bulky volume, the linear power supply apparatus is not applicable to a slim-type electronic device. In addition, the converting efficiency of the linear power supply apparatus is too low to comply with the power-saving requirements. In comparison with the linear power supply apparatus, the switching power supply apparatus has reduced volume but increased converting efficiency. That is, the switching power supply apparatus is applicable to the slim-type electronic device or long-term use.
Conventionally, a switching power supply apparatus comprises a front-stage power circuit, a back-stage power circuit, a bus capacitor and a standby power circuit. The front-stage power circuit and the back-stage power circuit are used for converting electric energy. The bus capacitor is electrically connected with the output terminal of the front-stage power circuit so that the bus capacitor is charged by the electric energy of the front-stage power circuit. In a case that the back-stage power circuit is disabled, the electric energy discharged from the bus capacitor may be provided to the back-stage power circuit so that the back-stage power circuit can continuously provide electric energy to the load for a hold-up time.
The standby power circuit is connected with the output terminal of the front-stage power circuit and the bus capacitor. By the standby power circuit, the electric energy outputted from the front-stage power circuit or the electric energy stored in the bus capacitor may be converted into a standby voltage. The standby voltage may provide electric energy required for powering the internal circuitry or electronic components of the power supply apparatus. For example, the internal circuitry or electronic components of the power supply apparatus includes the front-stage controlling circuit and the back-stage controlling circuit, which are used for controlling the front-stage power circuit and the back-stage power circuit, respectively. Consequently, the electric energy required to start the power supply apparatus may be provided by the standby power circuit.
As known, for allowing the electronic product to receive electric energy with high reliability, the power supply system is usually designed to have a redundancy configuration composed of plural power supply apparatuses. By the redundancy configuration of the power supply system, the electric energy provided by the plural power supply apparatuses are homogenized, and thus the overall electric quantity provided by the power supply system will be increased. Moreover, since the redundancy configuration of the power supply system is composed of plural power supply apparatuses, if one of the power supply apparatuses has a breakdown, the electronic product can be still enabled.
FIG. 1 is a plot illustrating the relationship between the power efficiency and the output electricity of a typical power supply apparatus. Although the redundancy configuration may increase the reliability of the power supply system, there are still some drawbacks. As shown in FIG. 1, when the power supply system provides electric energy to the electronic product in a light load condition, the overall operating efficiency is reduced. For example, if the power supply system has an (n+1) redundancy configuration, the power supply system comprises two power supply apparatuses. Under this circumstance, the electric energy provided by the first power supply apparatus to the electronic product and the electric energy provided by the second power supply apparatus to the electronic product are substantially equal. As shown in FIG. 1, when the power supply system provides electric energy to the electronic product in the light load condition (e.g. the power consumption amount of the electronic product is lower than 40 percentage of the rated power supply amount), the power efficiency of the conventional power supply apparatus is very low. Under this circumstance, the overall operating efficiency of the power supply system is deteriorated.
For solving the above drawbacks, a power supply system is designed to turn on or turn off specified power supply apparatuses according to the load condition in order to enable specified number of power supply apparatuses according to the power consumption amount of the electronic product. Although the power efficiency is increased and the reliability of the redundancy configuration is enhanced, the power supply system needs an additional power distribution unit for detecting the power consumption amount and determining the on/off statuses of the power supply apparatuses. Under this circumstance, the fabricating cost of the power supply system is increased.
Moreover, for reducing power loss to achieve the power-saving efficacy, the power supply apparatus should be instantly started when the power supply apparatus is turned off or in the standby status. For example, when the power supply apparatus is turned off or in the standby status, the back-stage power circuit is turned off but the front-stage power circuit is continuously enabled. In such way, the operating loss of the back-stage power circuit is reduced. Moreover, since the front-stage power circuit is continuously enabled, the front-stage power circuit can continuously provide electric energy to the standby power circuit and the bus capacitor. As such, the standby power circuit can continuously provide the standby voltage to the front-stage controlling circuit and the back-stage controlling circuit. After the back-stage power circuit of the power supply apparatus is turned on, the back-stage power circuit may be instantly enabled under control of the back-stage controlling circuit.
However, since the front-stage power circuit is continuously enabled when the power supply apparatus is turned off or in the standby status, the operating loss of the front-stage power circuit still exists. Under this circumstance, the power-saving efficacy of the conventional power supply apparatus is unsatisfied. Although the front-stage power circuit and the back-stage power circuit may be both turned off when the power supply apparatus is turned off or in the standby status, some problems occur. For example, since the standby power circuit is electrically connected with the output terminal of the front-stage power circuit and the bus capacitor, if the front-stage power circuit is turned off, the electric energy stored in the bus capacitor is converted into the standby voltage to power the front-stage controlling circuit and the back-stage controlling circuit by the standby power circuit. Since the front-stage power circuit is turned off, the front-stage power circuit fails to continuously provide electric energy to the bus capacitor for storage. Under this circumstance, the electric energy stored in the bus capacitor is reduced or exhausted because the electric energy is provided to the standby power circuit. For re-starting the power supply apparatus, a waiting time period is necessary to charge the bus capacitor by the front-stage power circuit. In other words, the power supply apparatus fails to be instantly started because of a response relay.
Therefore, there is a need of providing a power supply apparatus and a power supply system with plural power supply apparatuses so as to obviate the drawbacks encountered from the prior art.